As individual identification techniques for identifying the identify of an object such as an industrial product and a commercial product, various kinds are proposed and practically used; for example, a barcode, a serial number, and an IC tag. One of the individual identification technique is a technique to extract a feature quantity from an image obtained by imaging a random pattern on an object and consider the extracted feature quantity as an individual identifier of the object.
For example, Patent Documents 1, 2 and 3 describe techniques to use taggant (an additive for tracking) as fine particles, form a pattern containing the taggant on an object, image a predetermined area of the pattern, and consider the distribution of the particles in the predetermined area extracted from the image obtained by imaging as a feature quantity (an individual identifier of the object).
To be specific, in Patent Document 1, a taggants distributed pattern is formed entirely or partially on the surface of a reference object by applying printing ink containing taggants, and a feature quantity extracted from an image obtained by reading the taggants distributed layer is considered as an individual identifier of the reference object. At the time of verification of a target object, under the same reading conditions such as the orientation, position and range of reading as those for reading the reference object, an image of a taggants distributed pattern on the target object is read, and a feature quantity extracted from the image is compared with the individual identifier of the reference object.
Further, in Patent Document 2, an origin which becomes a reference for alignment is set on each object, a feature quantity is extracted from a predetermined area of a two-dimensional plane on which a rightward direction from the origin is a positive direction of an X-axis and a downward direction from the origin is a positive direction of a Y-axis, and the extracted feature quantity is considered as an individual identifier of the object. Herein, as the shape of the predetermined area, a rectangle, a circle, an ellipse, a polygon and another specific shape are shown as examples.
Further, in Patent Document 3, a reference portion is put on an object (the reference portion is, for example, an alignment mark, a line, a company logo, a frame, and an edge or a combination of edges of the object), and a coating material containing taggants, or the like, is sprayed and a random pattern is attached so as to completely cover at least the reference portion. Then, a feature quantity depending on the distribution of taggants is extracted from an image of the reference portion and is considered as an individual identifier of the object.
Further, a technique to perform individual identification by using a subtle difference of a product surface pattern for each individual is proposed. For example, in Patent Document 4, a feature quantity is extracted from an image of a predetermined area on a product defined with reference to a reference portion, which exists in common on products, and the extracted feature quantity is considered as an individual identifier of the product.
Furthermore, a technique disclosed by Patent Document 5 is a technique related to the present invention. In Patent Document 5, a label having a unique pattern is given to an object. Each label is manufactured by cutting a sheet or a film made of a polymer or the like having a unique pattern into a predetermined size. Moreover, each label has an identifier formed by a trademark or a logo.
Patent Document 1: Japanese Unexamined Patent Application Publication No. JP-A 2013-069188
Patent Document 2: Japanese Unexamined Patent Application Publication No. JP-A 2014-006840
Patent Document 3: Japanese Unexamined Patent Application Publication (Translation of PCT Application) No. JP-A 2007-534067
Patent Document 4: Re-publication of PCT International Publication No. WO2013/018614
Patent Document 5: US Patent Application Publication No. US2008/0197620A1
However, it is difficult to universally apply the abovementioned techniques disclosed by Patent Documents 1 to 4 to plural kinds of objects having different outer shapes and sizes from each other. This is because an area to extract a feature quantity is defined with reference to a reference portion on an object in the techniques disclosed by Patent Documents 1 to 4 and a portion which can be a reference portion on an object differs with the outer shape and size of an object.
On the other hand, the technique disclosed by Patent Document 5 can be applied to any objects that labels can be attached even if the outer shapes and sizes of the objects are different from each other. However, Patent Document 5 does not have an idea of “an area on a label defined with reference to some kind of reference portion” and therefore requires verification of a feature quantity extracted from an image of the whole label. Consequently, in a case where an object surface with a label attached has a color, a material, a pattern or the like which is hard to be visually distinguished from a pattern of the label, an image of the whole label cannot be specified and extraction of a feature quantity fails.